Scientists have identified a "dial" in the human brain that ramps up when we explore a new area — and the finding could help us understand why getting lost is often an early symptom of dementia, such as Alzheimer's disease.
Imagine you're walking a well-worn route home, but you accidentally take a wrong turn. It doesn't take long for your brain to sound alarms to tell you that you've gotten lost.
"When you move to a new city or travel somewhere, it doesn't happen that you just become familiar," study co-author Deniz Vatansever, a neuroscientist at Fudan University in China, told Live Science. "You have to explore your environment to become familiar with it." Vatansever and his team aimed to re-create this experience in VR.
They recruited 56 healthy volunteers ages 20 to 37, each of whom navigated a virtual world while inside a scanner. They explored the virtual environment — a grassy field surrounded by mountains — while looking for six "items" hidden throughout it. Vatansever's team monitored the volunteers' brain activity with functional MRI, a technique that tracks blood flow through the brain, as they explored familiar and unfamiliar areas of this world.
The team zoomed in on the hippocampus, a brain region that's important for memory and navigation. The seahorse-shaped hippocampus is rich with place cells, which light up in response to specific locations. Previous research had shown that one end of the hippocampus contains cells that fire when we think about location in a broad sense, such as where landmarks are in a nearby city. At the other end, place cells activate when we think about specific locations, like where we keep a box of cereal in our kitchen.
Between the "head" and "tail" of the hippocampus seahorse is a gradient of activity linking these broad and fine-tuned representations of locations. But no one had previously examined the organization of cells that respond to the newness or familiarity of a place.
Vatansever's team found that the head of the hippocampus contains cells that fired when their participants explored areas they had been in previously. Cells at the tail responded to new locations. And the whole region was arranged in a gradient, from familiar to unfamiliar.
"You could see that there's this shift in level of novelty versus familiarity as you go from one end to the other," Vatansever said.
Previous research produced mixed results on which areas of the hippocampus respond to novelty or familiarity in the environment, said Zita Patai, a cognitive neuroscientist at University College London who was not involved with the research. "What they're showing is that [the discrepancy] might partially be due to the fact that it's a gradient," she told Live Science.
Other brain areas also responded differently to new and familiar locations. A region in the cortex — the brain's higher-thinking hub — had a cone-shaped gradient. "At the very center of it are bits that 'prefer' more familiarity. And as you move out, then there is greater and greater preference for being active for novelty," Vatansever said.
The team also probed whether navigating familiar and unfamiliar areas activated broader brain networks, or groups of cells spread throughout the brain that often activate in sync. Familiar areas activated networks previously linked to motor control and memory, whereas novel areas activated networks associated with focus and perception.
This division may help the brain adapt to new environments by focusing on and absorbing relevant details, Vatansever said. Then, memory and motor control combine to help navigate familiar areas, he proposed.
The findings may explain some of the earliest signs of dementia, Vatansever suggested. The cells within the gradients in the cortex and hippocampus happen to be among the first brain areas affected by Alzheimer's disease. Both the front and rear regions of the hippocampus are equally vulnerable in the condition's early stages.
Louis Renoult, a cognitive neuroscientist at the University of East Anglia who was not involved with the research, said the paper demonstrated the strong links between navigation and memory.
The brain areas that help us navigate are also key for episodic memory, which relates to specific events in our lives rather than to factual knowledge, Renoult told Live Science. Episodic memory is also especially vulnerable in the early stages of Alzheimer's.
A better understanding of how navigation is encoded in the brain could reveal measurable signs of dementia's earliest stages, when the ability to navigate begins to falter.
"If you wanted to enhance people's ability to be independent, you'd want them to be able to go to new places and understand new things," Patai said. "In that sense, the link between spatial novelty and memory is really interesting."
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